Hydrogen based energy storage apparatus and method

ABSTRACT

Utility power is wheeled to distributed hydrogen energy storage systems during off peak periods where it is used in an electrolyzer to disassociate water into hydrogen and oxygen. The hydrogen at least is stored for use in a fuel cell or combustion engine driven generator to produce locally generated electricity during peak periods or power interruptions. Efficient electrolysis and gas storage are obtained by operating the electrolyzer at high pressures through two flow loops in which the hydrogen and oxygen produced in the electrolyzer pass to separate gas-water columns and force water into the electrolyzer. When the desired high pressure is reached, the gases are bled off into a series of storage tanks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the storage of energy for future use, and moreparticularly, to apparatus and a method for converting electrical energyduring off-peak periods of low demand to hydrogen and oxygen that arestored for later conversion back into electrical energy during peakperiods of high demand. It also relates to such a system and method thatoperates at self generated high pressure for efficient energy conversionand storage of the gases.

2. Background Information

Electric utilities have large installed capacity to met peak demand andthe required safety margin. Most of the time, especially at night andweekends, only a fraction of that capacity is required to meet nominaldemand. In fact, some of the peaking units operate only a few hours ayear. In addition, utilities purchase blocks of peak power on atake-or-pay basis to ensure sufficient power during their highest demandperiods, such as mid-summer heat waves. In some instances, bottlenecksin the transmission system complicate the task of delivering power whereit is needed during periods of peak demand.

In addition to the problems associated with economically meeting peakdemand, utilities have endeavored to improve performance through loadleveling in order to operate certain of their equipment at maximumefficiency. U.S. Pat. No. 6,093,306 describes a complex system forabating emissions and providing load leveling for fossil fuel plants.The process produces hydrogen through the electrolysis of water duringoff-peak periods for use in a fuel cell at the plant to generateelectricity during peak periods, which is added to the plant output.While this allows the fossil fuel plant to operate more efficiently andcleanly, it does not address the problems of transmission constrictionor peaking.

It has also been suggested that renewable energy sources, such as solarand wind energy, can be used to generate hydrogen gas which is then usedto generate electricity in fuel cells during periods when the sunlightor wind is not available or insufficient to produce electricity. Again,neither of these approaches address the problems of transmissionrestriction or peaking.

There is room, therefore, for improvements in the configuration andoperation of systems for generating and distributing electric power.

SUMMARY OF THE INVENTION

In accordance with the invention, electric energy generated by a primaryelectric power source is transmitted to a specified location remote froma utility generating station where it is stored by using it todisassociate water into hydrogen and oxygen, which are stored for laterconversion of at least the hydrogen into locally generated electricityin a hydrogen to electricity converter. The utility generatedelectricity is wheeled to the specified location, such as a user site, asubstation, or on a distribution line during off-peak periods and thestored gases are used to produce the locally generated electricityduring peak periods. Thus, the low cost power generated by the utilityduring low demand periods can be converted to higher value electricpower during peak periods. In addition, the adverse effects ofconstriction on the transmission system are ameliorated by reducing thetransmission capacity required during peak demand periods. Thisadvantage is enhanced by wheeling the utility generated power during lowdemand periods to a plurality of distributed specified locations remotefrom the utility generating station. Also, by providing distributedgeneration using stored gas, the effects of transmission interruptions,such as for example by storms, are mitigated.

As another aspect of the invention, the apparatus which generates thedeferred electric power comprises an electrolyzer energized by theprimary electric power source to disassociate water into hydrogen andoxygen, and a gas collection system that includes a first gas-watercolumn connected to the electrolyzer to form a first flow loop in whichthe hydrogen produced in the electrolyzer passes to the first gas-watercolumn and forces water from the first gas-water column into theelectrolyzer. This gas collection system further includes a secondgas-water column connected to the electrolyzer to form a second flowloop in which oxygen produced in the electrolyzer passes to the secondgas-water column and forces water from the second gas-water column intothe electrolyzer. A gas storage system stores the hydrogen from thefirst flow loop and the oxygen from the second flow loop. A hydrogen toelectricity converter, such as fuel cell or combustion engine drivengenerator, converts the stored hydrogen back into electricity usingeither the stored oxygen or ambient oxygen. In the later case, thecollected oxygen can be utilized or sold for other purposes. A valvingsystem maintains the pressure of the hydrogen and oxygen at a selectedpressure above about 1,000 psi by controlling the flow of hydrogen fromthe first flow loop and oxygen from the second flow loop to the gasstorage system. Thus, the apparatus operates at high pressure withoutadditional pressurizing equipment for efficient conversion and gasstorage. This pressure can be regulated to between about 2,500-5,000 psiwith the exemplary apparatus operating at about 3,000 psi.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the invention can be gained from the followingdescription of the preferred embodiments when read in conjunction withthe accompanying drawings in which:

FIG. 1 is a schematic diagram of an electric power system incorporatinga hydrogen-based energy storage system in accordance with the invention.

FIG. 2 is a schematic diagram of a basic embodiment of theelectricity-to-hydrogen converter section of the hydrogen-based energystorage system.

FIG. 3 is a schematic diagram of another embodiment of theelectricity-to-hydrogen conversion section.

FIG. 4 is a schematic view of a modified embodiment of the gas storageportion of the system.

FIG. 5 is a schematic diagram illustrating a distributed hydrogen-basedenergy storage system in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an electric power system 1 in which a primaryelectric power source 3 such as a utility generating station provideselectric power to a transmission system 5. The utility generating plant3 can be a fossil-fueled plant, a nuclear plant, a hydroelectric plantor a renewable power source such as a wind generator or solar generator.The source of the primary power provided to the transmission system isnot critical and there can be multiple primary power sources. Inaccordance with the invention, a hydrogen-based energy storage system 7is located at a specified location 9 on the transmission system 5.

The hydrogen-based energy storage system 7 includes anelectricity-to-hydrogen converter 11 energized by power provided fromthe transmission system 5 through an incoming power control andconditioning unit 13, which among other things, rectifies the multiphasetransmission line power. The electricity-to-hydrogen converter 11disassociates water provided through a water conditioning unit 15 intohydrogen gas and oxygen gas which are collected and stored separately ina gas storage system 17. In accordance with one aspect of the invention,electric power from the utility generating station 3 is wheeled over thetransmission system 5 to the hydrogen-based energy storage system 7 forconversion into hydrogen and oxygen during off-peak periods. At leastthe stored hydrogen is supplied during peak periods to ahydrogen-to-electricity converter 19 such as a fuel cell or a combustionengine driven generator to generate locally generated electricity, whichcan be supplied by an outgoing power control and conditioning unit 21back to the transmission system 5 to provide the peaking power. Inaddition to providing peaking power, the hydrogen-based energy storagesystem 7 helps to overcome the effects of bottlenecks in thetransmission system 5 during peak periods by providing distributedpower. Where the hydrogen-based energy storage system 7 is co-locatedwith a customer 23, the locally generated electricity can be added tothe electricity drawn by the customer directly from the transmissionsystem 5 to meet the power requirements of the customer during periodsof high demand. In addition, the hydrogen-based energy storage system 7can provide power to the transmission system and the local customerswhen there are interruptions in power delivery over the transmissionsystem such as during storm outages. The output control and conditioningunit 21 can include an inverter for converting the dc power produced bya fuel cell or by a combustion engine driven dc generator intomultiphase ac power. Typically, the combustion engine driven generatorwould have an ac output. The water produced as a byproduct by a fuelcell can be fed back to the electricity-to-hydrogen converter 11.

FIG. 2 illustrates in more detail the electricity-to-hydrogen converter11. This converter 11 includes an electrolyzer 25 which uses the dcelectric power provided by the power conditioning and control unit 13 todisassociate water into hydrogen and oxygen. A gas collection system 27includes a first gas-water column 29 which is connected to theelectrolyzer 25 through a pipe 31 to receive the hydrogen gas whichaccumulates at the cathode of the electrolyzer. A second pipe 33 betweenthe first gas-water column 29 and the electrolyzer 25 completes a firstflow loop 35 in which hydrogen produced in the electrolyzer 25 passes tothe first gas-water column 29 and forces water in the column into theelectrolyzer. The gas collection system 27 includes a second gas-watercolumn 37 is connected to the electrolyzer by an oxygen pipe 39 and awater pipe 41 to form a second flow loop 43 in which oxygen gas, whichaccumulates at the anode of the electrolyzer, passes into the secondgas-water column 37 and forces water from this second gas-water columnback to the electrolyzer. A control unit 45 operates valves 47, 49, 51and 53 in the pipes 31, 33, 39 and 41, respectively, to establish theseflow loops during gas generation by the electrolyzer 25. The controlunit 45 also monitors the pressure in the first gas-water column 29sensed by the pressure sensor 55 and the gas pressure in the secondgas-water column 37 sensed by the pressure sensor 57 for use incontrolling the operation of valves 59 and 61 that control the flow ofhydrogen and oxygen, respectively, to the gas storage system. Inaccordance with the invention, the pressure is permitted to build up toat least about 1000 psi, and for better efficiency, is maintained atabout 2,500 to about 5,000 psi. The exemplary system operates at about3,000 psi. This self-developed high pressure allows the electrolyzer 25to operate more efficiently and also provide for more efficient gasstorage without the need for separate pressurizing equipment.

The electricity-to-hydrogen converter 11 illustrated in FIG. 2 is abatch system. The first and second gas-water columns 29 and 37 arefilled to a specified level with water from a water supply system 63 bythe control unit 45 operating valves 65 and 67. As shown in FIG. 1, thewater for charging the gas-water columns 29 and 37 can include the waterproduced when a fuel cell is used as the hydrogen-to-electricityconverter as supplemented by an incoming water supply. Operation of theelectrolyzer 25 is terminated and the first and second gas-water columns29 and 37 are recharged when water level sensors 69 and 71 detect apredetermined low water level state.

In operation, when the gas-water columns 29 and 37 are fully charged,the valves 65 and 67 are closed while the valves 47, 49, 51 and 53 areopened. The valves 59 and 61 are initially closed. The electrolyzer 25is energized with the hydrogen gas produced flowing in the first loop 35into the first gas-water column 29 to force additional water into theelectrolyzer and with the oxygen similarly displacing water in thesecond gas-water column 37. When the gas pressures in the gas-watercolumns 29 and 37 build up to the desired high pressure, the valves 59and 61 are also opened to maintain that pressure by diverting the gasesto the gas storage system 17. When the low water level is sensed in thegas-water columns 29 and 37, the electrolyzer is de-energized and thevalves 47, 49, 51 and 53 are closed. The gas pressure is bled off andthe valves 59 and 61 are closed while the valves 65 and 67 are opened torecharge the gas-water columns with water.

FIG. 3 illustrates another embodiment of the electricity-to-hydrogenconverter 11 having a dual gas collection system 27′ that includes anadditional first gas-water column 29′ connected to the electrolyzer toform an additional first flow loop 35′ and an additional secondgas-water column 37′ similarly connected to the electrolyzer to form anadditional second flow loop 43′. These additional flow loops 35′ and 43′are formed by similar piping and valves as the first and second flowloops with the components identified by the same reference charactersprimed. With this arrangement, half of the gas collection systemcontaining a first gas-water column and a second gas-water column isavailable for collecting the gases produced by the electrolyzer whilethe other first gas-water column and the other second gas-water columnare being recharged. Electrolysis can be maintained continuously with atransition from one set of gas-water columns to the other.

FIG. 4 illustrates an embodiment of the gas storage system 17, whichincludes at least one hydrogen storage tank 77 that receives hydrogengas from the electricity-to-hydrogen converter 11 through the hydrogenline 73 and control valve 79. A non-return valve 81 prevents backfeedingof hydrogen and maintains the pressure of the stored gas. Similarly, anoxygen storage tank 83 receives oxygen from the electricity-to-hydrogenconverter 11 through the oxygen line 75, control valve 85, andnon-return valve 87. The hydrogen and oxygen are stored until neededwhereupon the valves 89 and 91 are opened to provide hydrogen and oxygento the fuel cell (or combustion engine driven generator) through lines93 and 95, respectively. Depending upon the requirements of the gasstorage system 17, a plurality of hydrogen storage tanks 79 ₂-79 _(n)and oxygen storage tanks 83 ₂-83 _(n) can in like manner be connected tothe hydrogen and oxygen supply lines 73 and 75 and the output lines 93and 95, respectively. As mentioned previously, at least the hydrogen isused to generate the locally generated electricity. The stored oxygencan also be used for this purpose or, where ambient oxygen is used inthe hydrogen-to-electricity converter, the stored oxygen can be used forother purposes or sold. While the hydrogen storage tanks 77 and theoxygen storage tanks 83 are shown in FIG. 4 as having the same volume,the tanks 83 can be half the volume, or be half as many as the tanks 77,because twice as much hydrogen as oxygen by volume is produced in thedisassociation of water. With the multitank system, the filled tanks canbe maintained at the high system pressure, e.g., about 3,000 psi, whilean empty tank for each gas is used to bleed off pressure from thegas-water columns 29 and 37 for recharging.

FIG. 5 illustrates an electric power system 1 in which three utilitypower plants 3 provide electric power to a power grid 97 throughsubstations 99. The grid 97 has numerous interconnected transmissionlines 101 providing power through additional substations 103 todistribution systems 105 servicing a number of customers 107. Inaddition to the problem of supplying sufficient power to meet therequirements of all the customers during peak periods, there can also beconstrictions in the grid transmission lines 101 which limit the abilityto meet all the needs of all of the customers during peak periods eventhough there may be sufficient capacity at the utility power plants. Foreither or both of these reasons, the system illustrated in FIG. 5 hasdistributed hydrogen-based energy storage systems 7 located throughoutthe network 97 remotely from the utility generating plants 3. Thesedistributed hydrogen-based energy storage systems can be separatelysited such as at 7 a, may be sited at a substation such as 7 b, orco-located with a customer such as at 7 c. With such an arrangement,electric power is wheeled to these distributed hydrogen-based energystorage systems 7 a-7 c where the hydrogen generated is stored for useduring periods of peak demand, when there are constrictions in thetransmission system and when there is interruption in the delivery ofutility generated power to a portion of the power grid.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of invention which is to be given the fullbreadth of the claims appended and any and all equivalents thereof.

What is claimed is:
 1. Apparatus for storing energy generated by aprimary electric power source and for regenerating electricity from thestored energy, the apparatus comprising: an electrolyzer energized bythe primary electric power source to disassociate water into hydrogenand oxygen; a gas collection system comprising: a first gas-water columnconnected to the electrolyzer to form a first flow loop in which thehydrogen produced in the electrolyzer passes to the first gas-watercolumn and forces water from the first gas-water column into theelectrolyzer; a second gas-water column connected to the electrolyzer toform a second flow loop in which oxygen produced in the electrolyzerpasses to the second gas-water column and forces water from the secondgas-water column into the electrolyzer; and a gas storage systemconnectable to receive and store hydrogen from the first flow loop andoxygen from the second flow loop; a hydrogen-to-electricity converterconnectable to receive at least hydrogen from the gas storage system andto generate electricity therefrom; and a valving system maintainingpressure of the hydrogen in the first flow loop and pressure of theoxygen in the second flow loop at a selected pressure above about 1,000psi by controlling flow of hydrogen from the first flow loop and oxygenfrom the second flow loop to the gas storage system.
 2. The apparatus ofclaim 1 wherein the valving system maintains the pressure in the firstflow loop and in the second flow loop at about 2,500-5,000 psi.
 3. Theapparatus of claim 1 wherein the valving system maintains the pressurein the first flow loop and in the second flow loop at about 3,000 psi.4. The apparatus of claim 1 wherein the gas collection system comprisesan additional first gas-water column forming an additional first loop inwhich hydrogen from the electrolyzer passes into the additional firstgas-water column to force water from the additional first gas-watercolumn into the electrolyzer, an additional second gas-water columnforming an additional second flow loop in which oxygen passes from theelectrolyzer into the second gas-water column to force water from thesecond gas water-column into the electrolyzer, and the valving systemincludes valving alternately connecting the first and second gas-watercolumns to the electrolyzer and then the additional first gas-watercolumn and the additional second gas-water column to the electrolyzer.5. The apparatus of claim 1 wherein the gas storage system comprises atleast one hydrogen storage tank and at least one oxygen storage tank. 6.The apparatus of claim 4 wherein the at least one hydrogen storage tankhas about twice the volume of the at least one oxygen storage tank. 7.The apparatus of claim 6 wherein the at least one hydrogen storage tankcomprises a plurality of hydrogen storage tanks and the at least oneoxygen storage tank comprises a plurality of oxygen storage tanks. 8.The apparatus of claim 1 wherein the hydrogen-to-electricity convertercomprises a fuel cell.
 9. The apparatus of claim 8 wherein the fuel cellreceives oxygen from the gas storage system as well as hydrogen for usein generating electricity.
 10. The apparatus of claim 1 wherein thehydrogen-to-electricity converter is a combustion engine drivengenerator.
 11. The apparatus of claim 10 wherein the combustion enginedriven generator receives oxygen from the gas storage system as well ashydrogen for use in generating electricity.